Effect of a fire plume on suppression spray droplet motion

The effect of a fire on the droplets from suppression systems plays an important role in the physics of fire suppression. Particle image velocimetry (PIV) was used to measure the droplet velocities from two nozzles and afire sprinkler in the presence of fires ranging from 5 to 50 kW. Results show that the droplet velocity field is highly dependent on fire size, with droplets having generally slower downward velocities over large regions of the spray as the fire size increases. In some small regions, the fire plume results in a reversal of the droplet velocity, indicating that droplets are carried upward. For the 50-kW fire, the fire overwhelms the spray. Droplet trajectories, determined by tracking typical droplets' progression in the spray fields, show that droplets are blown sideways away from the fire plume. Droplet tracking also shows that droplet penetration into the fire plume decreases as fire size is increased. The penetration depends on the ratio of spray drag to plume momentum.